In our daily life we often encounter some jobs which are best completed by moving in a back and forth manner. Examples of these are household chores such as sweeping, waxing, and mowing grass, farming which includes sowing, dunging, and reaping, and construction work which includes making terra cotta floors and painting, etc.. According to conventional methods, the worker will usually operate the tool or drive the apparatus in a back and forth manner on a surface of the specific work site. To obtain maximum efficiency, a minimum portion of the new working area should overlap slightly with the previously worked on area. For the automatic machine working on a specific area as in U.S. Pat. No. 4,919,224, the applicant developed a boundary-detecting device and a front-wheel steering device which control the vehicle movement between a boundary defining the working site. A set of wire sensors is applied to the device to detect the boundary of the working site in order to assure that the vehicle will turn when reaching the boundary in forward direction and proceed in the opposite direction. In another pending application Ser. No. 07,418,135, only a front-wheel steering device is applied to control the straight motion of the vehicle, and the deflecting angle of motion is to be detected and corrected by means of guide-line sensing.
In the U.S. Pat. No. 3,744,586, a flat surface is used as a reference surface to guide a moving machine. The machine is controlled to move straight by means which enable said machine to move along a flat surface. The turning movement of the machine is governed by a turning control device which controls the four wheels of the machine.
Unlike this prior art, the present invention provides two independent driving wheels such that each driving wheel can be driven forward or backwards to move the vehicle along the required trajectory. Also, the front of the vehicle always heads in the moving direction.
With regard to straight movement, the U.S. Pat. No. 3,744,586 requires a flat surface. However, in the present invention, the speed of the two driving wheels can be varied independently so as to keep the mileage of the wheels the same even when the vehicle encounters uneven surfaces. This control is closed loop control which is deemed to obtain better precision than the prior art.
With regard to turning and shifting a displacement, the U.S. Pat. No. 3,744,586 does not have means to turn its "head", instead, the vehicle directly moves backward and therefore the vehicle can be used in bi-directional machines only. However, the present machine can directly turn its "head" and shift in a displacement direction of the axis of the driving wheels. The movement of the machine is guided by a sensing apparatus which comprises odometers and guide line sensing modules, that is, the sensing modules generate feedback signals to the machine to indicate the required movement. In other words, the front of the machine always heads in the direction of movement and the present invention can be used in a simple unidirectional machine.